1. Field of the Invention
The present invention relates to electronic circuits and systems. More specifically, the present invention relates to electronic fuzes used in weapon systems.
2. Description of the Related Art
For many applications, there is a need to provide a fuze for a munition. For certain applications, a low-cost, passive proximity fuze is needed. For example, the Global Positioning System (GPS) is currently being used to provide accurate munitions guidance to target via a constellation of satellites. It is anticipated that the use of a plurality of low cost GPS transmitters may be deployed as a countermeasure to thwart the GPS guidance system of a missile or other munition in flight.
Hence, there is a need for a munition capable of homing in on and destroying a GPS jammer. The jamming transmitters would be small and elevated making destruction problematic. Low cost missiles are therefore currently being considered for this application. The missiles would be traveling at high speed and therefore would typically require both a guidance system and a fuze. The guidance system would steer the weapon to the target and attempt to impact it, and an RF fuze would be needed to fuze the weapon if it missed the target and the impact fuze does not function. This would add considerably to the cost of the munition in that a radar transmitter, receiver, and signal processor would typically be required. With respect to the passive fuze approach, no known RF fuze would suffice and an active fuze would be expensive in the requirement of a radar transmitter system or other active detection methodology.
Unfortunately, the interfering jammers are anticipated to be low cost jammers deployed in large numbers. Accordingly, the high costs associated with the above-described active fuze and precision guidance system approaches for the anti-jammer munition render these approaches impractical. In addition, the guidance system and the active fuze approaches would also adversely impact the form factor of the solution.
Hence, a need remains in the art for a low cost-effective alternative to allow for the use of an inexpensive munition to destroy small, inexpensive jamming signal source targets.
The need in the art is addressed by the passive proximity fuze of the present invention. The inventive fuze is adapted to be mounted on a munition and includes a receiver adapted to lock on to a signal transmitted by a jamming transmitter. The receiver detects a Doppler shift in the signal as the munition approaches the target. When a closest point of approach is reached the Doppler shift changes from increasing to decreasing. The inventive fuze includes a mechanism for detecting this change in the Doppler shift and provides a detonation signal in response thereto.
In the illustrative embodiment, the receiver is an FM receiver. The mechanism for detecting a change in the Doppler shift may be implemented with discrete analog circuitry or digital circuitry. In an illustrative analog implementation, first and second resistive/capacitive (RC) networks are employed to compute a second derivative of the Doppler shift signal output by the receiver. This signal is then amplified and thresholded to provide the output detonation signal.
In an illustrative digital implementation, the output of the receiver is converted to digital and processed by a digital signal processor (DSP). The DSP computes the second derivative of the Doppler shift signal output by the receiver in response to a stored program for computing same. The output of the DSP is the detonation signal. Hence, detonation is achieved at the closest point of approach of the munition to the target with an inexpensive passive solution.